Evaporation of R134a in flooded plate and shell heat exchanger systems

Abstract

The liquid chillers are refrigeration systems that remove heat from a secondary refrigerant. The secondary refrigerant, such as water, is then distributed to the location where refrigeration is needed. The main components of chiller are a compressor, an expansion valve and two heat exchangers: the evaporator and the condenser. The scope of this thesis was to research the chiller systems and the evaporation of the refrigerant 134a in the flooded plate and shell evaporator. The plate and shell heat exchanger consist of a plate pack inside a shell. The experimental research focuses on the effect of the plate surface roughness. The plates of the plate pack were roughened with glass ball blasting in terms of increased heat transfer. The tests were carried out with the R134a chiller plant and the thermosiphon system: first, using a standard plate pack and then, treated plate pack. No significant improvements in heat transfer coefficient were observed. However, the significant effect of the oil was noticed in the R134a chiller tests. The thermosiphon test was carried out with pure refrigerant (R134a and NH3) and, as a result, muchhigher heat transfer coefficients were achieved. The present technology of the chiller is concentrated on R134a, but it may be assumed that a shift towards natural refrigerants can take a place in near future. In the future research, more attention shall be focused on the applications used with natural refrigerants as well as the oil behaviour. The roughened plate surface does not prove to be beneficial in the heat transfer, thus, the research shall target on plate macro structure or pattern, to further improve the heat transfer.